Overweight and obesity have increased alarmingly in developed countries, reaching regarded as the biggest problem for public health in the XXI century. The aim of this study was to determine the prevalence of childhood overweight and obesity in a representative population of schoolchildren aged 10-11 years in Santiago (Chile). A cross-sectional study was conducted in a representative sample of 515 students enrolled in 4th and 5th year of Primary Education in the city of Santiago, Chile. Anthropometric measures identified were: weight, height, BMI, waist circumference, skinfold (triceps and subscapular) and percent body fat. Overweight and obesity were determined according to internationally established cut-off points. We found that 25% of students were overweight, 30% were obese while 45% were classified as normal weight. Girls showed a higher prevalence of normal weight (49.4% vs 40.7%) and overweight (26.7% vs 23.5%), while children showed higher prevalence of obesity than girls (35.8% vs 23.9%). These high prevalence of overweight and obesity underscore the need for intervention programs capable of reversing this situation, which should be focused on those at greatest risk